Medical or medically-oriented products constitute a large market for various polymeric materials, including nonwoven fabrics, as well as extrudable polymeric syringes, tubing, tissue culture flasks, packaging films, and the like.
At present, this market is generally dominated by latex-bonded polyesters and rayons, with polypropylene homopolymers and copolymers occupying a marginal role at best. This is due, to a great extent, to the need to expose such polymeric material to sterilizing doses of radiation, particularly gamma radiation in order to conveniently satisfy hygienic guidelines. A number of polymers, particularly polyolefin homopolymers and copolymers, however, are severely degraded or damaged by radiation exposure, causing unpleasant odor, discoloration, brittleness, and general loss of strength.
A number of additives such as hydrocarbon oils, halogenated hydrocarbon oils, phthalic acid esters, vegetable oils, silicon oils (Ref. U.S. Pat. Nos. 4,110,185, 4,274,932, 4,467,065), various organic carboxylic acids and organic phosphites (British Pat. No. 1,050,802), hindered phenol, and benzaldehyde stabilizers (U.S. Pat. No. 4,460,445) have been proposed and used in the art, with varying degrees of success, to minimize one or more of the above problems. None of such additives, however, capable of satisfactorily controlling long range damage due to sterilizing amounts of gamma radiation, particularly those products comprising fibers and/or films containing substantial amounts of polyolefin.
It is an object of the present invention to develop a method for obtaining radiation resistant polyolefin-containing products.
It is a further object of the present invention to increase resistance to gamma radiation-induced damage to polypropylene-containing fiber and film extrusion products.